Protein orders semiconductor
bits

January 28/February 4, 2004

Researchers working to make structures
at the size-scale of molecules are tapping self-assembly techniques found
in nature.

National Renewable Energy Laboratory researchers have found a
way to construct fairly complicated nanostructures by combining a genetically
engineered form of the protein cohesin with quantum dots. Cohesin is found
naturally in a microorganism that uses it to build side protein complexes
dubbed cellusomes; quantum dots are bits of semiconductor material that
can trap electrons.

The researchers' nanostructures have a combination of light-absorption
and electrical properties that could form the basis of a new generation
of solar cells.

The researchers formed the three-armed, or trefoil, structures
by causing the amino acid tags from the cohesin to interact with the zinc
sulfide shell of a cadmium selenide quantum dot, then subjecting the combination
to high-pressure chromatography, a technique for chemically separating
substances.

The protein-coated quantum dot structures have an average diameter
of 30 to 75 nanometers, which is 1,000 to 2,000 times narrower than a
human hair.

The researchers are working to create more complicated quantum
dot arrays. The ultimate goal is to self-assembled quantum dots arranged
in specific patterns and to control energy and charge transfer between
them in order to harvest energy from light, according to the researchers.